The present invention relates to a weather-resistant composition, a coating material containing the composition as a principal component, and a molded article.
Coating materials containing a (meth)acrylate compound as a coating film-forming component have widely been employed to protect the surface of a substrate because a cured coating film (hereinafter referred merely to as a xe2x80x9ccoating filmxe2x80x9d otherwise stated) thereof is superior in transparency, mechanical strength, surface smoothness, scratch resistance and close adhesion with molded articles made of various materials (hereinafter referred merely to as a xe2x80x9csubstratexe2x80x9d otherwise stated) and has high pencil hardness.
However, the coating film formed from the coating materials has such drawbacks that it causes discoloration or reduction in mechanical strength when exposed to ultraviolet light because of its poor weather resistance. Since the coating film formed from the coating materials is superior in transparency as described above, the substrate is also likely to be impaired by ultraviolet light, like the coating film.
To solve these drawbacks, an ultraviolet absorber is added to the coating material described above. Examples of the ultraviolet absorber include additive type ultraviolet absorbers such as benzophenone compound, benzotriazole compound, phenyl salicylate compound phenyl benzoate compound(various compounds such as those disclosed in Japanese Patent Laid-Open Gazette No. 56-127635), and cyanoacrylate compound. Among these ultraviolet absorbers, a benzotriazole compound having a wide absorption wavelength range is particularly useful.
However, any of the addition type ultraviolet absorbers described above had such problems that they are evaporated or decomposed by heating during formation of the coating film or are liable to bleed out from the surface of the coating film with a lapse of time due to rainwater, thereby making it impossible to provide a molded article with the weather resistance because they are low-molecular compounds and have poor heat resistance and poor compatibility with a resin as a coating film-forming component.
Accordingly, it is necessary to add a large amount of the addition type ultraviolet absorber in the coating material in light of loss of the ultraviolet absorber during and after formation of the coating film in order to provide the coating film with excellent weather resistance.
If a large amount of the addition type ultraviolet absorber is added in the coating material, it could cause such problems that the color of the coating film changes into ocher yellow due to an influence of light absorption thereby to impair the transparency, or cracks occur on the surface of the coating film or close adhesion between the coating film and the substrate is lowered.
The coating film containing the addition type ultraviolet absorber, especially a benzotriazole compound also has such a problem that, when it is contacted with a liquid or solid containing metal ions such as copper ion (more specifically, automobile wax and detergent), it changes the color of the coating film into brown thereby to drastically impair the transparency because of its high reactivity with metal ions (poor metal ion resistance). The reason is that a phenolic hydroxyl group in the benzotriazole compound reacts with metal ions to form a complex which can change the color of the coating film into brown.
Thus, Japanese Patent Laid-Open Gazette No. 4-372668 suggests, for example, a method of avoiding use of a large amount of an ultraviolet absorber by using two or more addition type ultraviolet absorbers having different maximum absorption wavelength ranges in combination, thereby improving the weather resistance while preventing the coating film from discoloring.
However, since two or more ultraviolet absorbers having different maximum absorption wavelength ranges are elected from the addition type ultraviolet absorbers and used in combination according to this method, the metal ion resistance of the coating film still remains poor and the ultraviolet absorber is liable to bleed out from the coating film so that the weather resistance of the coating film is not sufficiently improved. Accordingly, it is essential to use a large amount of the ultraviolet absorber to maintain good weather resistance for a prolonged period and, therefore, the above problems are likely to occur.
Japanese Patent Laid-Open Gazette Nos. 5-255447 and 5-271203 suggest a reaction type benzotriazole compound (reaction type ultraviolet absorber) represented by the general formula (2): 
[wherein X represents a hydrogen atom or a halogen atom, Ra represents a hydrogen atom, a methyl group, or a tertiary alkyl group having 4 to 6 carbon atoms, Rb represents a straight-chain or branched alkylene group having 2 to 10 carbon atoms, and Rc represents a hydrogen atom or a methyl group] in which a (meth)acryloyloxy group, as a functional group capable of copolymerizable with an ethylenically unsaturated monomer, is introduced into a molecule of the benzotriazole compound in place of the addition type ultraviolet absorber.
When the reaction type benzotriazole compound (2) is added in a coating material containing a coating film-forming component such as a radical polymerizable, ethylenically unsaturated monomer or oligomer capable of copolymerizable with a (meth)acryloyloxy group or a polymeric product thereof and the coating film-forming component is polymerized by heating after coating, the compound (2) is integrated by bonding (formation of a copolymer) with the resin after polymerization, thus making it possible to prevent it from bleeding out from the coating film.
When the copolymer of the reaction type benzotriazole compound (2) and the radical polymerizable, ethylenically unsaturated monomer is added in the coating material containing the coating film-forming component, not only the resulting coating material is superior in compatibility with the coating film-forming component, but also evaporation due to heating during the formation of the coating film is less likely to occur because of large molecular weight per se.
However, the compound (2) and the copolymer thereof is improved in the metal ion resistance as compared with the benzotriazole compound per se as a raw material but is not still improved sufficiently and when contacted with an automobile wax or detergent for a prolonged time, it gradually forms a complex with metal ions contained in the automobile wax thereby to change the color of the coating film into brown.
Japanese Patent Laid-Open Gazette No. 9-316060 describes a reaction type bisbenzotriazolylphenol compound (hereinafter referred to as a xe2x80x9cbisbenzotriazolylphenol compound (3)) represented by the general formula (3): 
[wherein Y is directly bonded or represents an alkylene group having 1 to 6 carbon atoms, a group of xe2x80x94C(CH3)2xe2x80x94, a group of xe2x80x94C(C2H5)(CH3)xe2x80x94, a group of xe2x80x94Oxe2x80x94, or a group of xe2x80x94NHxe2x80x94, R6 and R8 are the same or different and represent a hydroxyl group, or a straight-chain or branched hydroxyalkyl group having 1 to 12 carbon atoms, and R7 and R9 are the same or different and represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, an aryl group, an alkoxy group having 1 to 4 carbon atoms, or a halogen atom].
The bisbenzotriazolylphenol compound (3) can provide the coating film with excellent weather resistance by the addition of a smaller amount as compared with a conventional ultraviolet absorber because it has a structure of dimerized benzotriazolylphenol and has large ultraviolet absorbability per unit weight.
In addition, the bisbenzotriazolylphenol compound (3) does not bleed out from the coating film because a hydroxyl group other than a phenolic hydroxyl group in a molecule of the compound (3), e.g. reactive group such as hydroxyalkyl group, is integrated by bonding with the coating film-forming component such as (meth)acrylate compound. The bisbenzotriazolylphenol compound (3) is scarcely decomposed or evaporated by heating because of its large molecular weight.
The bisbenzotriazolylphenol compound (3) has such a structure that one benzotriazolylphenol in the same molecule serves as an adjacent bulky substituent to a phenolic hydroxyl group of the other benzotriazolylphenol, thereby to protect the phenolic hydroxyl group and to prevent the formation of a complex with metal ions. Accordingly, the reactivity with metal ions is very poor and, therefore, contact with an automobile wax or detergent for a prolonged period does not change the color of the coating film into brown.
However, the bisbenzotriazolylphenol compound (3) is inferior in the compatibility with a (meth)acrylate compound as the coating film-coating component and the solubility in an organic solvent used widely as an auxiliary component of the coating material so that the state of being dispersed in the coating material becomes uniform sometimes, thereby to impair the surface smoothness of the coating film and mechanical strength.
An object of the present invention is to provide a novel weather-resistant composition which can form a coating film which is not impaired in mechanical strength, exhibits excellent weather resistance, metal ion resistance and transparency for a prolonged period, and is less likely to cause surface cracks.
Another object of the present invention is to provide a coating material containing the weather-resistant composition as a main component, and a molded article coated with a coating film formed from the coating material.
The present inventors have intensively studied to solve the problems of the prior art described above and found a fact that coating of the surface of a substrate with a composition containing an ultraviolet absorber represented by the following general formula (1) and a specific (meth)acrylate compound makes it possible to form a coating film, which is not impaired in mechanical strength, exhibits excellent whether resistance, metal ion resistance and transparency for prolonged period, and is less likely to cause surface cracks, in the surface of the substrate. Thus, the present invention has been completed.
That is, the present invention provides a weather-resist composition comprising:
(I) a bisbenzotriazolylphenol compound as an ultraviolet absorber, which is represented by the general formula (l): 
xe2x80x83[wherein A is directly bonded, or represents a methylene group which have a substituent, a straight-chain or branched alkylene group having 2 to 6 carbon atoms, a group of xe2x80x94Cxe2x80x94, or a group of xe2x80x94NHxe2x80x94, and R1 and R2 are the same or different and represent a group (B): 
xe2x80x83(in which R5 is directly bonded, or represents a straight-chain or branched alkylene group having 1 to 12 carbon atoms, R3 and R4 are the same or different and represent a hydrogen atom or an alkyl group having 1 to 10 carbon atoms, m represents an integer of 1 to 20, and n represents an integer of 4 to 8)];
(II) at least one (meth)acrylate compound as a coating film-forming component, which is selected from (meth)acrylate monomer and (meth)acrylate oligomer; and
(III) a curing agent; a coating material containing the weather-resistant composition as a main component; and a molded article, partial or whole surface of which is coated with the coating material.
The bisbenzotriazolylphenol compound (hereinafter referred to as a xe2x80x9cbisbenzotriazolylphenol compound (1)xe2x80x9d) of the general formula (1) used as the ultraviolet absorber in the present invention can provide the coating film with excellent weather resistance by the addition of a smaller amount as compared with a conventional ultraviolet absorber because it has a structure of dimerized benzotriazolylphenol and has large ultraviolet absorbability per unit weight, like the bisbenzotriazolylphenol compound (3) disclosed in the aforementioned Japanese Patent Laid-Open Gazette No. 9-316060.
Therefore, according to the weather-resistant composition containing the bisbenzotriazolylphenol compound (1) as the ultraviolet absorber according to the present invention, it is made possible to form a coating film which exhibits excellent weather resistance while maintaining excellent transparency as described above and is less likely to cause surface cracks.
The bisbenzotriazolylphenol compound (1) has such a structure that two benzotriazolylphenols in the same molecule serve as adjacent bulky substituents to a phenolic hydroxyl group of the other benzotriazolylphenol, thereby to protect the phenolic hydroxyl group and to prevent the formation of a complex with metal ions, which can change the color of the coating film into brown, due to poor reactivity with metal ions.
Accordingly, the coating film formed by using the coating material comprising the weather-resistant composition of the present invention is superior in metal ion resistance for a prolonged period and is less likely to change the color into brown.
Since the bisbenzotriazolylphenol compound (1) has a large molecular weight and a high decomposition temperature (excellent heat resistance) as compared with a conventional ultraviolet absorber because of its structure of dimerized benzotriazolylphenol as described above, it is not evaporated or decomposed by heating during the formation of the coating film.
Since the bisbenzotriazolylphenol compound (1) has a large molecular weight and also has a reactive group (B) (long-chain polyester group) capable of being integrated by bonding with the coating film-forming component in a molecule, it is made possible to prevent it from bleeding out from the surface of the coating film more securely.
Accordingly, the coating film formed by using the coating material comprising the weather-resistant composition of the present invention is superior in weather resistance and transparency for a prolonged period.
Furthermore, the long-chain polyester group of the bisbenzotriazolylphenol compound (1) is remarkably superior in the compatibility with the (meth)acrylate compound as the coating film-forming component and the solubility in an organic solvent, thereby scarcely impairing the surface smoothness and mechanical strength of the coating film as well as close adhesion with the substrate. Accordingly, even if a large amount of the bisbenzotriazolylphenol compound (1) is added in the coating material, it does not exert an adverse influence on the transparency and mechanical strength of the coating film, like a conventional ultraviolet absorber.
According to the weather-resistant composition of the present invention, it is made possible to provide the coating film with remarkably excellent metal ion resistance, weather resistance and transparency for a prolonged period without impairing original properties of the coating film containing the (meth)acrylate compound as the coating film-forming component, i.e. excellent transparency, mechanical strength, surface smoothness, wear resistance, scratch resistance, and close adhesion with the substrate. Also the weather-resistant composition of the present invention can provide the coating film with excellent chemical resistance for a prolonged period.
Therefore, even if the coating film formed by using the coating material comprising the weather-resistant composition of the present invention is exposed to factors accelerating deterioration of the coating film, e.g., ultraviolet light, automobile wax or detergent, for a prolonged period, discoloration of the coating film as well as lowering of the mechanical strength and the close adhesion with the substrate do not occur. Therefore, the coating film is very useful to protect the substrate.